JP2733776B2 - Thin plate continuous casting method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a twin-roll type continuous sheet casting apparatus for continuously casting a sheet directly from a molten metal and a method of operating the same.

[Background of the Invention and Prior Art] A pair of internal cooling rolls whose axes rotating in opposite directions are horizontal are arranged in parallel and opposed to each other with an appropriate gap, and a roll circumferential surface above this gap (along the roll axis). A so-called twin-roll type continuous machine in which a pool is formed on the upper body surface of the cylindrical surface in the direction and the molten metal in the pool is continuously cooled to a thin plate through the gap while being cooled by a rotating roll circumferential surface. Casters are known. It has been proposed to apply such a twin-roll type continuous casting machine to continuous casting of steel to directly produce thin steel sheets from molten steel.

In such a twin-roll type continuous casting machine, a solidified shell is formed on the roll circumferential surface in contact with the molten metal, and this is rolled by a roll gap. However, the solidified shell formed on the roll circumferential surface is Since the growth occurs at a large temperature difference between the low temperature side of the roll surface and the high temperature side of the molten metal, a strain is generally generated by thermal stress or the like due to the temperature difference, thereby causing a part to be separated from the roll surface. That is,
A partial gap occurs between the solidified shell and the roll surface. In the part where the adhesion between the solidified shell and the roll surface is released, the presence of the gap reduces the heat conduction,
The cooling of that part is less than that of the contact part. Therefore, the solidification speed from the molten metal is reduced, and the shell thickness is partially reduced. Poorly cooled portions caused by such causes often cause cracks on the surface of the thin plate when subjected to stress due to thermal shrinkage during cooling after casting.

[Problems to be solved by the invention]

In order to prevent the surface crack of the thin plate due to the uneven cooling as described above, one effective means is to slow down the cooling by the roll and reduce the thermal stress of the solidified shell by the slow cooling. As means for slow cooling of the roll, it is also useful to coat a ceramic coating with low thermal conductivity on the circumferential surface of the roll, or to use the ceramic roll itself. However, in this case, it is liable to be broken during casting and has a problem in terms of life.

Further, if the roll surface is uniformly roughened by sand blasting or the like, the roughened surface forms a heat insulating layer and can be cooled slowly, whereby cooling unevenness can be reduced and surface cracks can be prevented. However, there is a problem that the rough surface of the roll is transferred to the cast sheet, and an irregular pattern remains on the sheet surface when the sheet is cold-rolled.

SUMMARY OF THE INVENTION The present invention aims at solving such a problem in twin-roll type continuous sheet casting, and aims to prevent surface cracks caused by uneven cooling during formation of a solidified shell and a pattern of a cold-rolled product, thereby achieving a high yield. It is an object of the present invention to provide a method for producing a thin sheet of high quality.

[Means to solve the problem]

According to the present invention, a pair of cooling rolls rotating in opposite directions are arranged in parallel to face each other, and a solidified shell is formed on a circumferential surface of the roll pair from a molten metal in a pool formed on a circumferential surface of the roll pair. In the continuous sheet casting method in which this solidified shell is pressed down into a thin plate in the gap between the roll pairs while forming a roll, the circumferential surface that comes into contact with the molten metal of the roll pair has a surface roughness Ra of 4 to 50.
The thin plate slowly cooled by the air gap layer evenly formed on the rough surface while passing through the gap between the pair of rolls with the rough surface in the range of μm It is characterized in that the sheet is continuously passed and the rough surface transferred to the thin plate surface is smoothed by the hot roll. In other words, the surface of the chill roll is made to have a surface roughness with an appropriate roughness, thereby uniformly reducing the heat conduction between the solidified shell and the roll surface to cool slowly, and causing the thin plate surface crack. To eliminate uneven cooling of the solidified shell, and smooth the rough surface transferred to the thin plate when passing through the roll gap under light pressure with a hot rolling roll installed in-line on the downstream side of the twin roll type. It is characterized in that the cause of pattern generation in cold rolling is eliminated in advance. The rolling reduction at the hot rolling roll may be in the range of 1 to 20%, and the position where the hot rolling roll is installed is such that the thin plate that has passed through the gap between the cooling roll pair still maintains a high temperature and the casting speed changes. Should be set to a position that can respond to.

Hereinafter, the contents of the present invention will be specifically described with reference to the drawings.

[Detailed Description of the Invention]

FIG. 1 shows an example of a twin-roll continuous caster to which the present invention is applied. In FIG. 1, reference numerals 1a and 1b denote a pair of internal cooling rolls which are opposed to each other so that they rotate in opposite directions (the rotation directions of both are indicated by arrows) with their axes horizontal, and 2 denotes these rolls 1a and 1b. In the pool formed on the circumferential surface R, 3a and 3b are side dams, and 4 is a thin plate to be cast.

In the example shown in the figure, a water-cooled roll is used for each of the roll pairs 1a and 1b for internal cooling. More specifically, each of the roll pairs 1a and 1b has a groove-like cooling water passage formed inside the roll sleeve forming the circumferential surface R (not shown in the figure). ), The circumferential surface R is cooled to a predetermined temperature by passing water through the cooling water passage. The supply and discharge of the cooling water to the cooling water passage inside the circumferential surface R are performed from a roll shaft. For this reason, the roll shaft is formed in the shape of a double pipe, the inner pipe of which is a cooling water supply pipe, the annular pipe formed between the outer pipe and the inner pipe is a drain pipe, The cooling water supply pipe is connected to a cooling water passage inlet inside the circumferential surface R, and the annular pipe is connected to a cooling water outlet. When cooling water is continuously supplied from the pump P to the inner pipe by this configuration as shown in the figure, the cooling water circulates through the cooling water passage inside the circumferential surface R and is drained through the annular pipe. This operation of passing the cooling water can be continued while the device is operating. Circumferential surface R that comes into contact with the molten metal of roll pair 1a, 1b
Is a rough surface within the range defined in the present invention by sandblasting or the like.

FIG. 2 shows a line until a thin plate 4 continuously manufactured from the twin-roll continuous caster of FIG. In the present invention, one stand of the hot rolling rolls 5a and 5b is arranged in this inline. The hot rolls 5a and 5b should be placed close to the rolls 1a and 1b so that the temperature of the cast sheet does not drop below a specified value, and the rolls should be capable of responding to changes in casting speed. The position is away from the pair 1a, 1b. Therefore, the pair of rolls 1a, 1b and the hot rolls 5a,
The rotation speed of 5b should be roughly synchronized, but the thin plate between the roll pair 1a, 1b and the hot rolled rolls 5a, 5b should flow with some play, not under tension. Is desirable. In some cases, it is more preferable to provide a looper or the like. Guide rolls 6a and 6b and pinch rolls may be provided between the roll pairs 1a and 1b and the hot rolls 5a and 5b as necessary. May be arranged. The thin plate that has passed through the hot rolling rolls 5a and 5b is transported by a transporting means such as a roller table 7 or a belt conveyor, and wound by a winding roll 7 to form a coil.

FIG. 3 schematically shows a rough surface state of the circumferential surface R of the pair of rolls 1a and 1b. The surface of the roll sleeve 10 in contact with the molten metal is formed as a rough surface 11 having irregularities. A solidified shell 12 is formed from the molten metal 2 on the rough surface 11. This rough surface
If 11 is evenly formed on the entire surface in contact with the molten metal by, for example, sand blasting, an ultra-thin air gap layer consisting of a gas layer taken into the unevenness of the rough surface is evenly formed between the roll surface and the shell 12. , Which has a heat insulating effect and is slowed down. As a result, the temperature difference between the surface and the inside of the shell 12 is reduced, the thermal stress acting on the shell 12 is also reduced, the phenomenon that the shell 12 is partially separated from the roll is reduced, and the thickness variation due to this is also reduced.

The present inventors have conducted various experiments and found that the roll circumferential surface R
At least the surface of the part in contact with the molten metal in the pool
It was found that if the surface was rough within the range of Ra = 4 to 50 μm, the cooling unevenness of the thin plate was reduced and the surface cracks could be prevented. Ra means the average roughness on the reference plane (center line) of the JIS standard (for example, JIS B 0601).

On the other hand, when such a rough roll is used, when the solidified shell 12 is rolled in the narrowest portion of the roll pair 1a, 1b,
The rough surface is transferred to the sheet surface. If a thin plate with this rough surface is subjected to cold rolling or other treatments as it is, slight fluctuations in plate thickness (undulation) due to slight unevenness in cooling may cause the rough surface of the plate surface to be crushed well or not. all right. This appears as an irregular pattern on the cold rolled sheet surface.
The irregular pattern disappears when a polishing step is performed, but the cost increases.

The present inventors have studied various countermeasures against this problem. As a result, when the thin sheet exiting the continuous sheet casting machine is subjected to light hot rolling at a still high temperature, the sheet surface roughness becomes considerably fine, and the sheet thickness is slightly reduced. It was found that there were no significant fluctuations, the plate thickness could be made uniform, and this problem could be solved by simple processing. The reduction ratio of this light hot rolling is preferably in the range of 1 to 20%. If it is less than 1%, the effect of improving the surface roughness is insufficient, and if it exceeds 20%, the rough surface of the thin plate is crushed or slightly cooled. The rolling reduction becomes too large to eliminate the slight thickness fluctuation due to unevenness, resulting in excessive equipment. Therefore, the light hot rolling equipment of the present invention does not aim at a large pressure reduction, but improves the surface quality of a sheet as much as a skin pass. The temperature of the sheet during light hot rolling differs depending on the type of molten metal, and cannot be said unconditionally. For example, in the case of molten stainless steel, SUS304 is suitable at 700 to 1250 ° C, and SUS430 is approximately 700 to 1230 ° C.

As described above, according to the present invention, the problem of the surface cracks of the cast plate and the problem of the quality deterioration due to the rough surface are effectively solved by minimizing the fluctuation of the thermal stress due to the temperature difference of the solidified shell. However, the thin sheet continuous casting apparatus to which the present invention is applied is not limited to the example of the illustrated upper pouring twin roll machine, but can also be applied to an oblique pouring twin roll machine or a different diameter twin roll machine.

〔Example〕

500kg SUS304 steel using a twin-roll thin-plate continuous caster consisting of a 400mmφ × 300mmW internal water-cooled copper alloy sleeve roll.
Was cast into a thin plate having a thickness of 2 mm. The circumferential surface of the roll was sandblasted to a roughness of Ra = 5 μm. The sheet was lightly hot-rolled in-line when the temperature of the sheet reached 1000 ° C to 1100 ° C, and then wound to form a coil. The rolling reduction of light hot rolling was 3%. As a result, the roughness and flatness of the coil surface before cold rolling were greatly improved, and the irregular pattern disappeared from the surface of the cold rolled sheet, resulting in an extremely good surface texture. No surface cracks were observed.

[Brief description of the drawings]

FIG. 1 is a perspective view of a main part of a twin-roll type continuous sheet casting machine for carrying out the method of the present invention, and FIG. 2 is a schematic cross-section showing a line from a continuous casting machine to a winding machine for carrying out the method of the present invention. FIG. 3 and FIG. 3 are conceptual views for explaining slow cooling by roughening the roll surface in a twin-roll continuous caster. 1a, 1b …… Internally cooled roll, 2 …… Molten in the pool, 3…
… Side dam, 4… cast thin plate, 5a, 5b… light hot roll, 8… winding machine, 11… rough surface of twin roll, 12… solidified shell.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Morikawa 4976 Tomita, Odai, Shinnanyo-shi, Yamaguchi Pref. Nishin Steel Corporation Shunan Laboratory (72) Inventor Tomoaki Kimura 3-1-1 Stock, Hitachi-cho, Hitachi-shi, Ibaraki Hitachi, Ltd. Hitachi Plant (72) Inventor Tadashi Nishino 3-1-1, Sachimachi, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Hitachi Plant (56) References JP-A-60-184449 (JP, A) JP-A Sho 62-254953 (JP, A) JP-A-60-83745 (JP, A)

Claims (2)

(57) [Claims] 1. A pair of cooling rolls rotating in opposite directions are arranged in parallel to face each other, and solidified from a molten metal in a pool formed on a circumferential surface of the roll pair onto a circumferential surface of the roll pair. In the continuous sheet casting method in which the solidified shell is pressed down into a thin plate in the gap between the roll pairs while forming the shell, the circumferential surface that comes into contact with the molten metal of the roll pair has a surface roughness Ra of 4 to 50.
A thin plate having a rough surface in the range of μm and slowly cooled by an air gap layer evenly formed on the rough surface while passing through the gap between the pair of rolls is heated under a low pressure of one stand while still maintaining a high temperature. A twin-roll type thin sheet ream, characterized in that the hot rolled roll smoothes the rough surface transferred to the thin sheet surface by continuously passing the sheet between the rolls to reduce the lightness at a rolling reduction of 1 to 20%. Casting method. 2. A pair of cooling rolls rotating in opposite directions are arranged in parallel and opposed to each other, and solidified on a circumferential surface of the roll pair from a molten metal in a pool formed on a circumferential surface of the roll pair. In a continuous sheet casting apparatus in which the solidified shell is pressed down to a thin plate in the gap between the roll pairs while forming the shell, a circumferential surface that comes into contact with the molten metal of the roll pair has a surface roughness Ra of 4 to 50.
The thickness of the thin plate passing through the gap between the pair of rolls is maintained at a high temperature, and the thin plate is lightened at a rolling reduction in the range of 1 to 20% at a position capable of coping with a change in casting speed. A twin-roll thin-sheet continuous casting apparatus, comprising a single-stand hot-rolling roll for reducing the pressure.